1. Field of the Invention
The present invention relates to the copyright protection, and in particular to a reproduction apparatus, in which the storage mediums being legally sold and distributed, as well as, being legally recorded can be reproduced therefrom, while bringing the mediums being illegally copied unable to be reproduced therefrom, and relates to a decoding apparatus, in which the codes which are reproduced from the storage mediums being legally sold and distributed and legally recorded therein can be decoded, while bringing the codes reproduced from the mediums being illegally copied unable to be decoded therefrom.
2. Description of Prior Art
As technologies relating to a video signal processing apparatus for certainly giving a protection under the copyright on video signals of high quality which can be obtained from video discs, digital VTRs, receivers for digital broadcasts and so on, a video signal processing method and recording mediums therefor, are disclosed, for example in Japanese Patent laying-Open No. Hei 10-178656 (1989). Also an authentication and key exchanges for copy protection is disclosed in NIKKEI ELECTRONICS 1998.3.23 (NO.712) P47-P53.
In the above patent laying-Open is disclosed, in particular a technology for copying protection by using a generation management information. However, it does not mention the technology for making unable the reproduction of storage mediums which are produced illegally.
For practicing such the copy protection with certainty, an encryption technology is very effective. Contents or information of video and audio to be recorded into the storage medium is encrypted, while a key for encryption is supplied only to a licensee, thereby enabling to make the reproduction of the storage medium which was produced illegally impossible or disabled.
However, once being reproduced by decrypting the code thereof, the contents of video and audio can be recorded freely into other storage medium(s), therefore it is impossible to practice the copy protection with certainty therewith. For protecting from such the copy, a technology of watermark is effective, in which a generation management information is superimposed onto the video and audio information in such a manner that they cannot be detected even if they are tried to sense visually and audibly. Namely, restricting the recording of the reproduced video and audio contents by detecting the watermarks thereof, or restricting the reproducing of the reproduced video and audio contents by detecting the watermarks thereof, it can be applied for protecting from the illegal copy, or from viewing the video and audio contents which are illegally copied.
Applying the technologies, such as of the encryption and the watermarks together, it is possible to practice the copy protection with higher certainty. Namely, it is enough that the watermarks are necessarily attached to the video and audio contents to be protected under the copyright and are necessarily encrypted on the storage medium. However, according to the conventional art, there is not paid enough considerations on a manner how to make unable the reproduction of the storage medium which was illegally produced in a case where the technologies of the encryption and the watermarks are applied together thereto. In particular, there is no consideration on a problem that the storage mediums, being legally sold and distributed or being legally recorded, may also be unable to be reproduced therefrom by erroneous detection of the watermarks thereof.